Generally, an object can be moved through space with six degrees of freedom. In other words, the object can be moved along six different axes, three of which are linear axes, and three of which are rotational axes. The three linear axis are commonly known as the x-axis, y-axis and z-axis. An object's movement through space from one point to another can be tracked along the three linear axes, x, y and z. However, that same object can twist, i.e. pivot or rotate, about each of the linear axes. Thus, there are three rotational degrees of freedom that are commonly represented by three rotational axes, referred to as the a-axis, b-axis and c-axis. The rotational axes sometimes also are known as roll, pitch and yaw.
It should be noted that rotational movement or rotational degrees of freedom of movement of the object are understood as rotation of the object about the linear axes, x, y, z extending through the object. Reference to the restriction of rotational movement of the object does not imply that the object cannot be moved along arcuate or circular paths from one point to another in space. Such arcuate or circular travel can be defined solely as movement along the three linear axes if no twisting of the object occurs.
Depending on the requisite manipulation of an object, machines are designed to move various objects through space with one to six degrees of freedom. For example, machine tools used for milling, drilling, and grinding workpieces are sometimes designed to manipulate an object, e.g. a cutting tool, along all six axes. However, many applications only require the object be moved with the three degrees of freedom defined by the three linear axes. In fact, in both situations, it often is undesirable to allow any twisting or rotational movement of the object, e.g. tool, because this can lead to poorly formed parts that do not meet modem tolerance requirements. This is particularly true with machines that generate substantial force loads, such as loads that occur during milling or drilling operations.
To combat the undesirable twisting and to maintain operational accuracy and precision, many three-axis machines use large cast components that move along precisely ground ways. The large, cast components reduce twisting of the object being moved, e.g., a spindle head for a drill or milling cutter. Simultaneously, the ways guide the heavy cast machine structures as they are moved along the x, y and z axes. Typically, such a machine includes a separate machine structure and a separate way or ways for each axis of movement. This leads to increased time and expense in building and maintaining the machine. Additionally, because of the mass of the solid machine structures, these machines are relatively slow in moving an object from one point to another.
The present invention addresses the foregoing drawbacks of existing three-axis machines.